The invention relates to a method of operating a mobile paver to compact an asphalt mix, and more particularly to a method of compacting a layer of asphalt material containing a mixture of particle of larger and smaller sizes.
Asphalt mix with a high coarse-grain proportion (in particular order of magnitude 30 mm or more) with at the same time a lack of or reduced proportion of medium grain size is problematic during paving using pavers which have at least one tamper and an adjoining screed, since the coarse grain at the surface of the paving layer, does not remain embedded on all sides in the mix of smaller grain size, but approximately crescent-shaped openings of greater or lesser width occur after the coarse grain, seen in the direction of travel of the paver. These openings can no longer be closed even by subsequent roller compaction.
In pavers of this type, the tampers usually have a metering slope in order to act in a metering manner on the mix to be used f or paving, in which case, in the event of tampers of this type being used as a pair, the front tamper in the direction of travel brings about precompaction to a lower height than the subsequent tamper which, however, likewise operates in a metering manner, while subsequently smoothing takes place by the screed and, if appropriate, additional compaction.
It is assumed in general that loose paving material is compacted by about 25% by a paver and, if appropriate, by subsequent rolling in order to achieve the paving state. In many cases, this final compaction cannot be achieved by a paver alone, which uses tampers and a screed, as is the case in a paver according to EP-A-0 115 567, but requires additional rolling to bring about approximately 5 to 10% of the compaction which, however, depends on the paving material. The loose paving material is usually applied with a layer thickness between about 3 and 30 cm (also depending on the type of paving material) and compacted, i.e. the total compaction is approximately within the range of 0.8 to 8 cm (=maximum stroke of the pair of tampers which is essentially halved between the front and rear tamper). In this case, this range is divided over the metering slope range of the pair of tampers in such a way that, f or example, in the upper position of the tampers, the metering slopes adjoin one another, i.e. essentially lie in a common plane. If this were not observed and if there were to be a considerable deviation therefrom, there would be the risk that the screed would be lifted out of its floating position and would not be able to undertake its smoothing function. Correspondingly, the rule also results: large strokes of the tampers for large layer thicknesses and small strokes of the tampers for small layer thicknesses, in each case with a staggered stroke setting of the tampers, arranged one behind the other, in the direction of travel.
Working in this manner, with asphalt mix, crescent-shaped openings form in the surface, as was described at the beginning, which openings can no longer be closed by rolling. Varying the tamper strokes within the range of the rules given to the person skilled in the art does not eliminate this problem. Higher paving temperatures or specific layer thicknesses or changes to the vibration amplitude of the screed or changes to the stroke frequency of the tampers, for example, do not achieve the objective either.
The foregoing illustrates limitations known to exist in present paving methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.